1. Field of the Invention
The invention relates in general to a touch sensing device, touch sensing apparatus, and a touch sensing method thereof, and more particularly, to a touch sensing device and touch sensing apparatus that is able to switch between an idle mode and an active mode using a touch sensing method thereof.
2. Description of the Related Art
Touch sensing apparatuses are now prevalent in various applications. Based on known sensing principles, touch sensing apparatus are generally categorized into resistive, capacitive, ultrasonic, and optic (infrared) types. Among the above types, a capacitive touch panel features relatively high light transmittance since materials thereof are nearly transparent, such as glass. Moreover, a transparent conductive film made of indium tin oxide (ITO) in a capacitive touch sensing apparatus offers better durability, and therefore the capacitive touch sensing apparatuses have become widely adopted.
In short, an operating principle of a capacitive touch sensing apparatus is that, a coordinate (position) of a touch point is detected according to induced current of a capacitance change caused by distortion of a static electricity field resulting from the combination of a transparent electrode and a human body upon contact. More specifically, when a user finger touches a surface of a touch sensing device, due to the conductivity of the human skin, a capacitance change between transparent electrodes is incurred by a user press. Such an electric change is transmitted to a touch sensing device, which accordingly calculates position information of the touch point.
Based on different types of sensing capacitors, approaches that a capacitive touch sensing apparatus obtains a touch position may further be categorized into a self capacitance calculation approach and a mutual capacitance calculation approach. A main difference between these two approaches is that, the self-capacitive detection is based on a capacitance change generated at all X-direction electrodes or all Y-direction electrodes, whereas the mutual-capacitive detection is based on a capacitance change occurring at an electrode overlapping region of electrodes.
FIG. 1A shows a schematic diagram of sensing a touch position through mutual capacitance between electrodes of different directions by implementing a double-layer touch sensing apparatus according to the prior art. A first plane and a second plane of the capacitive touch sensing apparatus respectively include a plurality of transparent electrodes. Between the two planes lies a dielectric layer for forming the mutual capacitance between the electrodes.
Referring to FIG. 1A, the first plane includes twelve parallel transparent electrodes X1 to X12 arranged and extended along the horizontal direction (X direction); the second plane includes eight parallel transparent electrodes Y1 to Y8 arranged and extended along the vertical direction (Y direction). The horizontal (X-direction) transparent electrodes are isolated from the vertical (Y-direction) transparent electrodes by the dielectric layer.
Between each X-direction transparent electrode and each Y-direction transparent electrode forms a mutual capacitance Csignal. Thus, in FIG. 1A, 12*8=96 mutual capacitances are formed at overlapping regions of the electrodes for sensing and positioning a touch. For example, between the transparent electrode X1 and the transparent electrode Y1 is an electrode overlapping region P11, on which a mutual capacitance is formed. Similarly, a mutual capacitance on an electrode overlapping region P22 is formed by the transparent electrode X2 and the transparent electrode Y2.
FIG. 1B shows waveforms of the horizontal driving electrodes while being sequentially applied a drive voltage in a conventional mutual-capacitive touch sensing apparatus. For brevity, assume the X-direction transparent electrodes X1 to X12 are driving electrodes, being sequentially driven under the control of the touch sensing device.
Assuming the drive voltage is 3V, a 3V voltage is respectively applied to the transparent electrodes X1, X2, . . . , X12 in the X direction. More specifically, when the transparent electrode X1 is driven by the 3V voltage, the remaining transparent electrodes in the X direction are not provided with the drive voltage. Similarly, for the remaining driving electrodes, when one of the X-direction transparent electrodes is driven, the rest of the transparent electrodes are not driven.
The Y-direction transparent electrodes Y1 to Y8 are sensing electrodes for sensing mutual capacitance changes. The voltage level sensed by the sensing electrodes when the touch sensing apparatus is not pressed is different from that sensed by the sensing electrodes when the touch sensing apparatus receives a press. Relationships of the voltage level sensed by the sensing electrodes, the touch point and the mutual capacitance shall be described with reference to FIG. 10.
FIG. 10 shows a schematic diagram of voltage driving and voltage sensing on the mutual capacitance formed at an electrode overlapping region of the transparent electrodes X1 and Y1 according to the prior art. The Y-direction sensing electrode Y1 and a reference voltage Vref are respectively coupled to a negative input and a positive input of an amplifier. Between the negative input and the positive input of the amplifier is a feedback capacitance Cfb with a predetermined and known capacitance value. Between the X-direction driving electrode X1 and the Y-direction sensing electrode Y1 is a mutual capacitance Csignal, whose capacitance value changes when a touch occurs thereupon. Further, an output voltage Vout is coupled to an analog-to-digital converter (ADC) for measuring the voltage.
It can be seen from FIG. 1B that, a 3V voltage is sequentially applied to the X-direction electrodes in a scanning process. Taking the electrode overlapping region P11 as an example, when the driving electrode X1 is driven, the voltage level of the sensing electrode Y1 changes as the value of the mutual capacitance Csignal decreases when voltage sensing is performed on the sensing electrode Y1.
Therefore, by measuring the voltage of the Y-direction sensing electrodes, it may be determined whether a touch event takes place. When a touch event takes place, a voltage difference between two ends of the mutual capacitance Csignal changes accordingly. Based on the known capacitance value of the feedback capacitance Cfb, the capacitance change of the mutual capacitnace may be obtained through an equation ΔVout=−Vy*(Csignal/Cfb) according to the measured outputted voltage Vout and the voltage level (3V) of the sensing electrode Vy1, so as to further provide position information of a touch point.
FIG. 2A shows a schematic diagram of a conventional touch sensing apparatus operating under an active mode for detecting a mutual capacitance change between electrodes. A first plane includes a plurality of first-direction electrodes X1 to X12; a second plane includes a plurality of second-direction electrodes Y1 to Y8.
A transparent dielectric layer 101 (a dielectric layer) is disposed between the first plane and the second plane. When a touch event occurs, corresponding electricity changes are generated at overlapping regions of the first-direction electrode and the second-direction electrodes in response to the touch event. That is, the capacitance value of mutual capacitance is changed due to the touch event.
For brevity, the driven transparent electrodes are indicated as shaded driving electrodes, whereas the transparent electrodes that are not driven are indicated as unshaded driving electrodes. Similarly, the sensing transparent electrodes are indicated as shaded sensing electrodes, whereas the transparent electrodes that are not sensing are indicated as unshaded sensing electrodes. Further, to distinguish the driving electrodes from the sensing electrodes, the sensing electrodes are more densely shaded than the driving electrodes.
In the conventional technique, when the touch sensing apparatus is in an active mode, the first-direction electrodes (driving electrodes) located on the first plane are sequentially and cyclically driven. Thus, for the whole touch panel, to perform a complete scanning process of an image, a drive voltage is applied sequentially to the driving electrodes X1 to X12, followed by again scanning toward the driving electrode X1 after having scanned toward the driving electrode X12.
FIG. 2B shows a schematic diagram of a conventional touch sensing apparatus operating in a standby (idle) mode for detecting a mutual capacitance change between electrodes. In the standby (idle) mode, the touch sensing apparatus does not sequentially drive all the driving electrodes or sense all the sensing electrodes. Alternatively, the touch sensing apparatus selectively drives corresponding driving electrodes and senses corresponding electrodes according to positions of sensing regions 11, 12, 13, and 14.
Assume that the touch sensing apparatus only provides a user with the four sensing regions 11, 12, 13, and 14 in an idle mode. The touch sensing apparatus only proceeds with subsequent processes when at least one of the four sensing regions is touched. That is, only when a touch event is sensed and confirmed at the sensing regions, the touch sensing apparatus switches the operating mode from the idle mode to the active mode.
An example is shown in FIG. 2B, the four sensing regions respectively include overlapping regions formed by the driving electrodes X2, X5, X8, and X11, and the sensing electrodes Y7 and Y8. While operating in the idled mode, the touch sensing apparatus only selectively scans the four sensing regions where the driving electrodes X2, X5, X8, and X11 pass through.
It is concluded from the above descriptions that, in the idle mode, the conventional technique needs to drive a corresponding number of driving electrodes according to the number of touch sensing regions. That is, in the idle mode, in order to determine whether a touch event takes place, the conventional technique needs to apply the drive voltage to the four transparent electrodes X2, X5, X8, and X11 and respectively scan the transparent sensing electrode Y7 when the four transparent electrodes X2, X5, X8, and X11 are driven. Yet, such approach is rather power consuming especially when there is a large number of sensing regions. Therefore, there is a need for a solution to the above issues.